Current supply device for a gas-and/or vapour discharge lamp

ABSTRACT

The invention relates to a device for supplying an intermittent current to a gas- and/or vapour discharge lamp. According to the invention an intermittent current is used in which the effective period is considerably shorter than the subsequent rest interval, whilst the pressure in the discharge space of the lamp is chosen to be comparatively high. This combination of a short effective period and a high pressure together with an appropriate choice of the frequency provides on the one hand a high light output of the lamp and on the other hand a long lifetime thereof. The potential increases in luminous efficiency provided by the invention is considerable.

United States Patent 1191 1111 3,745,41 1 Polman et ai. 1 1 July 10,1973 [5 CURRENT SUPPLY DEVICE FOR A 3,075,123 l/1963 Faulds 315 209 RGASANDIOR VAPOUR DISCHARGE LAMP 1,996,520 4/1935 Marshall, Jr... 315/209R 1 3,061,744 /1962 Spira 315/209 R X Inventors: J Polman; J rt a e3,310,708 3/1967 Seidler 315/209 R x Were, both of Emmasingel, 3,265,9308/1966 Powell, Jr. 315/209 R Eindhoven, Netherlands [73] Assignee: U.S.Philips Corporation, New York, Primary miner-Nathan KaufmanAtt0rneyFrank R. Trlfarl [22] Filed: Nov. 3, 1970 [57] ABSTRACT [21]Appl. No.: 86,471

The 1nvent1on relates to a dev1ce for supplying an intermittent currentto a gasand/or vapour discharge lamp. [301 Forelgn Apphcatmn Pnomy DataAccording to the invention an intermittent current is Nov. 10, 1969Netherlands 6916934 used in which the effeciive period is considerablyshorter than the subsequent rest interval, whilst the [52], [1.8. CI315/209 R, 315/272, 315/201 pressure in the discharge Space of the lampis chosen [51] Int. Cl. H05b 37/02 to be comparatively high Thiscombination Of a short [58] Field of Search 315/172, 209 R, 272,effective period and a high pressure together i an 315/246, 224, 98;313/109 appropriate choice of the frequency provides on the one hand ahigh light output of the lamp and on the [56] References Clted otherhand a long lifetime thereof.

UNITED STATES PATENTS The potential increases in luminous efficiencyprovided 2,538,062 l/ll TOUVCI 3l5/20l X by the invention isconsiderable, 2,525,900 8/1970 Skirvin et a1 315/98 3,536,945 10/1970Skirvin 313/109 X 6 Claims, 3 Drawing; Figures PATENIEUJUHOW I 3.745.411

Fig.3

JAN POLMAN JAN E. VAN DER WERF 2 1: AGE

CURRENT SUPPLY DEVICE FOR A GAS-AND /OR VAPOUR DISCHARGE LAMP Thisinvention relates to a device comprising a lowpressure gas and/or vapourdischarge lamp, in which two input terminals of the device are connectedto each other by a series combination of at least the lamp and aswitching element, the latter being connected to a control-device whichcontrols said switching element so that the lamp is traversed by anintermittent current, in which a time interval of W seconds during whichthe lamp is traversed by current is followed by an at least equallylong, substantially idle, time interval of R seeonds.

The term low pressure is to denote herein a pressure of at the most 150Torr.

A known device of the kind set forth is disclosed in French Pat.specification Nr. 1,456,460. This known device has the advantage of acomparatively high luminous efficiency (for example, expressed inLumen/- Watt). In the embodiment described in said French Pat.specification the time W is equal to the time R. If, in order toincrease the light output, the ratio W/(W+R) were chosen to be lowerthan one-half, while the lamp power is kept constant, the current peaksmight have such a high intensity that material would soon sputter fromthe electrodes of the lamp. This could be detrimental to the lifetime ofthe lamp.

An object of the invention is to provide a device in which the luminousefficiency of the discharge lamp is very high and also the lifetime ofthe lamp is long.

A device according to the invention, comprising a low-pressure gasand/or vapour discharge lamp in which two input terminals of the deviceare connected to each other by a series combination of at least the lampand a switching element, the latter being connected to a controLdevicewhich controls said switching element so that the lamp is traversed byan intermittent current, in which a time interval of Wseconds duringwhich current passes through the lamp is followed by an at least equallylong, substantially idle, time interval of R seconds, is characterizedin that in order to obtain a condition favourable for the production oflight the pressure in the discharge space is at least 4 Torr and is inaddition so high that the condition 7,; 1,, is fulfilled and in that theratio W/( W+R) is lower than 0.4 and in that the duration of a periodW+R of the supply to the lamp has a value lying between 21r TE and 271 1wherein:

T3 is the energy relaxation time (in seconds) of the electrons in thedischarge space and 7,, is the diffusion time (in seconds) of theelectrons in the discharge space.

The term energy relaxation time is to be understood to mean herein:l/A.B, wherein:

A is the average fractional energy loss per collision of an electron(fractional is to denote herein that the energy loss is expressed in theenergy of the electron prior to the collision), and

B is the average number of collisions of an electron with non-electronparticles in the discharge space per second.

The term diffusion time is to denote herein the time (expressed inseconds) required on an average by an electron to reach the wall of thedischarge space.

The device embodying the invention has the advantage that the luminousefficiency may be very high owing to the comparatively low value of theratio between the current time interval (W) and the substantially idletime (R) on the one hand and a given range of the period (W R) on theother hand, and because a lamp having a comparatively high pressure inthe discharge space is used. It is a further advantage that thecomparatively high pressure in the discharge space counteractssputtering from the lamp electrodes. in a device embodying the inventionthe lamp may therefore have a long lifetime.

The invention is furthermore based on the recognition that with thechosen period W+ R the electron gas cools down during the idle timeinterval by collisions until it has reached the temperature of theneutral gas, while during this time interval the electron concentrationhas diminished only slightly. The extent of concentration drop isdetermined by the diffusion time T which is longer than the timeinterval (W+R)/2w.

The current pulse following an idle time interval reheats the electrongas and it is found that then a comparatively large number ofhigh-velocity electrons is obtained, that is to say a number larger thanis obtained in a corresponding situation with direct-current operationof the lamp by the same average current. The efficiency of a gasdischarge is favourably affected by the presence of a comparativelylarge number of highvelocity electrons.

The discharge space may contain a rare gas, for example, argon, and/or ametal, for example, mercury.

In an advantageous device embodying the invention, in which the gas inthe discharge space is neon, the pressure of the neon is of the order of5 to 25 Torr, while the ratio W/( W+R) is at the most 0.3 and theduration W+R of a period of supply to the lamp lies between 4.10 and50.10" sec.

This preferred device has the advantage that with a suitably chosenpressure the obtainable light output may even be as much as six timesthat obtained with a direct current supply (the lamp power being thesame).

The invention will be described more fully with reference to theaccompanying drawing, wherein FIG. 1 shows a circuit arrangement of adevice embodying the invention;

FIG. 2 shows a further embodiment of a circuit arrangement of thedevice; and

FIG. 3 shows a further embodiment of the circuitry of the device.

Referring to FIG. 1, reference numerals I and 2 designate connectingterminals for a direct-current source of, for example, 200 V. Theterminals 1 and 2 are connected by a series combination of a dischargelamp 3, a series resistor 4 and the main electrodes of a transistor 5.The base of the transistor is connected to a pulse generator 6. Ajunction between the lamp 3 and the emitter of the transistor 5 also isconnected to the pulse generator 6. The pulse generator 6 is fed viaconnecting terminals 7 and 8, connected to an altemating-current supplyof 220 V, 50 Hz.

The pulse generator 6 is adjusted so that pulses of a duration of about25 p.866 are produced, each pulse being followed by an idle period ofabout usec.

The lamp 3 was a neon lamp having an operating voltage of about V (withdirect-voltage supply). The length of this lamp was about 750 mms andthe diameter was 36 mms. The pressure of the neon gas was about 10 Torr.The electrode material was tungsten with a barium oxide coating.

In this practical case the frequency l/(W+R) was about 8,000 Hz. 1' wasabout 1,000 psec and T was about 2.5 usec. The sum W+R was about 125sec. Thus the condition that W+R should lie between 21r TD and Zn 1 isfulfilled. Furthermore W/( W+R) is 0.2.

In order to compare this supply with other supplies of the lamp, thefollowing table indicates data for midnary direct current supply and forthe case of W/( W+R) 0.5 and finally for the case in which W/( W+R) 0.2.The latter figure is in accordance with the invention. The table showsthe case in which the neon pressure was Torr and the case in which theneon pressure was 5 Torr in a comparable lamp. The numbers in this tableindicate the relative lumen values of the lamps under the variousconditions expressed in percentages of the lumen value of the 5-Torrlamp driven by direct current. (The lumen value of the latter lamp wasabout 540 lumens with direct-current supply with a lamp power absorptionof 45 W). The frequency was 8 kHz in the cases of the extreme right-handcolumn and of the second extreme right-hand column. In all casesindicated in the table the lamp power was 45 W.

From these results it will be apparent that the lamp embodying theinvention (see the last column) has a higher luminous efficiency(expressed, for example, in lumen/Watt). It appears furthermore thatwith a higher pressure the increase in efficienvy is even higher thanwith a low pressure. This higher pressure also brings about a reducedsputtering of electrode material of the lamp.

The lifetime of the indicated lamps embodying the invention was notshorter than that of known discharge lamps with direct-current supply.

If it is desired to supply current to the lamp from a low-frequency A.C.supply, the transistor 5 may be included in a rectifying bridge (diodes10 to 13) as is shown in FIG. 2. In FIG. 2 reference numeral 3designates the lamp and 6 denotes the pulse generator.

With current supplied from a low-frequency A.C. supply, two transistorsmay be used which are included in parallel branches and have oppositepass directions. This is illustrated in FIG. 3. The transistors aredesignated by reference numerals l5 and 16. A diode l7 and a diode 18are connected in series with the transistors 15 and 16, respectively.The bases of the transistors 15 and 16 are connected to a pulsegenerator 6". The emitters of the two transistors are also connected tothe pulse generator 6". The lamp to be operated is designated by 3". Thediodes l7 and 18 serve to protect the transistors.

In the cases shown in FIGS. 2 and 3, a number of current pulses in onedirection through the lamp, each followed by rest intervals, is followedby a number of current pulses in the other direction through the lamp,each also followed by rest intervals. This is due to the fact that inthese cases the current is supplied to the lamp from a low-frequencyA.C. source, i.e., one having a frequency lower than 100 Hz, whereas thepulse generators control the transistors with a considerably higherfrequency, i.e., about 8,000 I-Iz.

In the examples described one pulse generator controls one lamp circuit.However, one pulse generator may be employed for controlling more thanone lamp circuit (as indicated by the series connection I, 4, 5, 3, 2 inFIG. I), so that to control the supply control of a group of lamps onlyone pulse generator is required.

What is claimed is:

1. An electric discharge lamp supply system comprising, a pair of inputterminals adapted for connection to a source of electric power, anelectric discharge lamp having a gas or vapor filling at a pressure ofat least 4 Torr and high enough to satisfy the condition that TE TDwherein:

TE is the energy relaxation time (in seconds) of the electrons in thelamp discharge space and 7,, is the diffusion time (in seconds) of theelectrons in the lamp discharge space,

a controlled switching element connected in series with the lamp acrosssaid input terminals, a control device connected to a control input ofthe switching element for switching said element to cause anintermittent flow of current to said lamp during a time interval Wfollowed by a time interval R which is at least as long as the timeinterval W and during which no current flows to the lamp, said controldevice operating the switching element so that the duty cycle W/( W+R)is lower than 0.4 and the duration of the lamp period W R is limited tothe range of values lying between 21m; and 21m 2. A system as claimed inclaim 1, the gas in the lamp discharge space is neon, characterized inthat the neon pressure is of the order of 5 to 25 Torr and in that W/(W+R) is at the most 0.3 and the duration W+R of a period of the supplyto the lamp lies between 4.10 and 50.10 seconds.

3. A system as claimed in claim 1 adapted for connection to analternating voltage power source of a frequency lower than Hz andcharacterized in that the switching element comprises a transistorincluded in a diagonal branch of a rectifying bridge having inputterminals connected in series with the lamp and the device inputterminals.

4. A system as claimed in claim 1 adapted for connection to analternating voltage power source of a frequency lower than 100 Hzancharacterized in that the switching element comprises the combinationof two transistors connected in parallel with the transistors havingopposite pass directions.

5. A system as claimed in claim 1 wherein said control device comprisesa pulse generator supplying trigger pulses to said switching element ata frequency of approximately 8,000 Hz.

6. A high efficiency low pressure electric discharge lamp comprising asealed glass envelope with a pair of spaced apart electrodes, a pair ofexternal terminals connected to said electrodes and adapted forconnection to a source of intermittent lamp supply current that suppliescurrent for a time period of W seconds followed by an off period of Rseconds at least as long as the time interval W, the pressure in thedischarge space being at least 4 Torr and high enough to satisfy thecondition 1 r,, the lamp supply frequency being restricted to a range offrequencies such that W/( W+R) 0.4 and the time period W+R lies between21r'r and 21",, wherein:

1 is the energy relaxation time (in seconds) of the electrons in thelamp discharge space and TD is the diffusion time (in seconds) of theelectrons in the lamp discharge space.

i it ii 1 mg UNITED S'IAlES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3,745,411 Dated July 10, 1973 Invent-or(s) JAN POLMAN ET ALIt is certified that error appears in the above-identified patent. andthat said Letters Patent are hereby corrected as shown below:

col. 1, line 22, before "time" (lst occurrence) insert "on" before"time" (2nd occurrence) insert "off" line 47, before'"sup ly" insertelectric lines 51 & 53, after "the" insert lamp col. '2, line 34, before"supply" insert electric line 58, after "Hz" insert (not shown) col." 3,line 18, after "with" (1st occurrence) insert a I after "supply" insertand t i In the claims, col. 4, line 39, cancel "device" and insertsystem Signed and sealed this 16th day of July 1974. k

1 (SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. An electric discharge lamp supply system comprising, a pair of inputterminals adapted for connection to a source of electric power, anelectric discharge lamp having a gas or vapor filling at a pressure ofat least 4 Torr and high enough to satisfy the condition that Tau E< TauD wherein: Tau E is the energy relaxation time (in seconds) of theelectrons in the lamp discharge space and Tau D is the diffusion time(in seconds) of the electrons in the lamp discharge space, a controlledswitching element connected in series with the lamp across said inputterminals, a control device connected to a control input of theswitching element for switching said element to cause an intermittentflow of current to said lamp during a time interval W followed by a timeinterval R which is at least as long as the time interval W and duringwhich no current flows to the lamp, said control device operating theswitching element so that the duty cycle W/(W+R) is lower than 0.4 andthe duration of the lamp period W + R is limited to the range of valueslying between 2 pi Tau E and 2 pi Tau D.
 2. A system as claimed in claim1, the gas in the lamp discharge space is neon, characterized in thatthe neon pressure is of the order of 5 to 25 Torr and in that W/(W+R) isat the most 0.3 and the duration W+R of a period of the supply to thelamp lies between 4.10 5 and 50.10 5 seconds.
 3. A system as claimed inclaim 1 adapted for connection to an alternating voltage power source ofa frequency lower than 100 Hz and characterized in that the switchingelement comprises a transistor included in a diagonal branch of arectifying bridge having input terminals connected in series with thelamp and the device input terminals.
 4. A system as claimed in claim 1adapted for connection to an alternating voltage power source of afrequency lower than 100 Hz ancharacterized in that the switchingelement comprises the combination of two transistors connected inparallel with the transistors having opposite pass directions.
 5. Asystem as claimed in claim 1 wherein said control device comprises apulse generator supplying trigger pulses to said switching element at afrequency of approximately 8,000 Hz.
 6. A high efficiency low pressureelectric discharge lamp comprising a sealed glass envelope with a pairof spaced apart electrodes, a pair of external terminals connected tosaid electrodes and adapted for connection to a source of intermittentlamp supply current that supplies current for a time period of W secondsfollowed by an off period of R seconds at least as long as the timeinterval W, the pressure in the discharge space being at least 4 Torrand high enough to satisfy the condition Tau E< Tau D, the lamp supplyfrequency being restricted to a range of frequencies such that W/(W+R)<0.4 and the time period W+R lies between 2 pi Tau E and 2 pi Tau Dwherein: Tau E is the energy relaxation time (in seconds) of theelectrons in the lamp discharge space and Tau D is the diffusion time(in seconds) of the electrons in the lamp discharge space.